This invention relates to a double flow-type condensing turbine installation and specifically is intended to improve the plant thermal consumption factor.
A conventional double flow-type condensing turbine installation, as shown in FIG. 1, includes a double flow-type steam turbine 1, a steam pipe 53 adapted to introduce steam from the central portion of the steam turbine 1 into the right and left turbine sections 3 and 2, a single pressure-type condenser 4 for condensing exhaust steam from the turbine sections 2 and 3, a cooling water pipe 5 of the condenser 4, a condensation pump 6 for returning condensation from the condenser 4 to a boiler (not shown), and a generator 7 coupled to the steam turbine 1. In this case, the right and left turbine sections 3 and 2 are symmetrical in configuration and accordingly they have the same steam path area in the turbine final stage and vane length. The exhaust outlets of these turbine sections 2 and 3 are combined into a single unit at the condenser 4.
In the double flow-type condensing turbine installation thus constructed, steam, for instance, from a high pressure turbine, is introduced through the steam pipe 53 into the right and left turbine sections 3 and 2. The steam, after expanding to perform work in the turbine sections 2 and 3, is supplied to the condenser 4 where it condenses into water which is returned into the boiler by means of the condensation pump 6. In this case, it is desirable that the degree of vacuum of the condenser be set as high as possible in order to recover, as much as possible, the energy of the steam as useful power.
Shown in FIG. 2 is a conventional multi-flow exhaust-type, here a four-flow exhaust-type, condensing turbine installation employed in a large scale heat power plant or a nuclear power plant.
In the condensing turbine installation, steam from a boiler (not shown) is supplied through a main steam pipe 101 into a high pressure turbine 102, steam exhausted by the high pressure turbine 102 is introduced into a reheater 103, the reheated steam of which is supplied to a middle pressure turbine 104. Exhaust steam from the middle pressure turbine 104 is introduced into a plurality of low pressure turbines 105 and 106 which are of like configuration. As each of the low pressure turbines 105 and 106 is a double flow-type steam turbine, the condensing turbine installation described above is a four-flow type steam turbine. Steam flows discharged by the steam turbines 105 and 106 are delivered in a parallel mode to a single pressure-type condenser 107 where they are condensed into water which is then returned to the boiler by a condensation pump 108. The degree of vacuum of the condenser 107 is set as high as possible so as to recover as much as possible of the energy of steam as power. In FIG. 2, reference numeral 109 designates a cooling water pipe and reference numeral 110 designates a generator.
In the conventional condensing turbine installation described above, the degree of vacuum of the condenser is determined from the rise of temperature of the cooling water in the condenser and the minimum final temperature difference (the saturated steam temperature in the condenser minus the temperature of cooling water at the outlet) which is actually achieved. The limit of the final temperature difference is 2.8.degree. C. as usual in Japan and the United States. It is difficult to provide a final temperature difference more than that. Accordingly, heretofore, the vacuum pressures of the single pressure-type condensers 4 and 107 of the above-described double flow-type condensing turbine installations had to be determined under the conditions mentioned above. Thus, with the above-described single pressure-type condenser, it is difficult to recover much of the energy of the steam with the results that the plant thermal consumption factor is low and the fuel expense is increased. This is one of the difficulties accompanying a conventional condensing turbine installation.
In order to eliminate this difficulty, a method has been proposed in the art, in which, as shown in FIG. 3, a double pressure-type condenser 117 is coupled to multi-flow exhaust-type steam turbines 105 and 106 which are similar in construction to those shown in FIG. 2. In this case, in comparison with the single pressure-type condenser 107 in FIG. 7, the total cooling area (Fc.sub.1 +Fc.sub.2) of the condenser 117 is set equal to the cooling area Fc of the single pressure-type condenser 107. Therefore, steam discharged by the steam turbine 105 is delivered to a high vacuum side condensing chamber 117I while steam from the steam turbine 106 is supplied to a low vacuum side condensing chamber 117II while the cooling water flows in series through the condensing chambers 117I and 117II through a pipe 119. However, as the logarithmic temperature differences of the condensing chambers 117I and 117II are small in this case, the final temperature differences .DELTA.T1 and .DELTA.T2 of the condensing chambers 117I and 117II are larger than the final temperature difference .DELTA.T of the single pressure condenser. Therefore, the degree of vacuum of the condenser 117I is improved. However, the degree of vacuum of the condenser 117II is made worse than that in the case of the single pressure type condenser. Thus, the overall improvement in the thermal efficiency of the installation is low as a whole.
In FIG. 4, reference characters ti, tm and to designate the inlet temperature, the middle temperature and the outlet temperature of the cooling water, respectively while ts and Fc designate respectively the saturated steam temperature and the cooling area of the single pressure-type condenser 107 and ts.sub.1 and Fc.sub.1 and ts.sub.2 and Fc.sub.2 the saturated steam temperatures and the cooling area of the condensing chambers 117I and 117II of the double pressure-type condenser 117, respectively. In FIG. 4, the curve A (dashed line) and the curve B (solid line) indicate the increasing variations of the cooling water in the single pressure-type condenser 107 and the double pressure-type condenser 117, respectively.